RU2211343C1 - Method of and plant for recovery of heat in contact-type steam-gas plant - Google Patents

Abstract

FIELD: power engineering. SUBSTANCE: proposed method of heat recovery in contact-type steam-gas plant includes compression of air in multistage compressor, delivery of said air, steam and fuel for combustion into combustion chamber, delivery of steam-gas mixture, thus formed, into steam-gas turbine, cooling of mixture used in steam-gas turbine in waste heat recovery boiler, delivery of steam formed in boiler for injection into combustion chamber and steam-gas turbine. Steam-gas mixture. after waste heat recovery boiler, is directed into regenerator maintaining temperature of mixture at inlet within 125 and 140 C and pressure within 4.2 and 6.5 kg/sq.cm. Steam formed in regenerator is delivered into condensing steam turbine and air condenser connected with regenerator by condensate line. Multistage turboexpander is installed after regenerator in direction of flow of steam-gas medium. Multistage turboexpander is provided with drop mixture separators between its stages and at outlet connected by condensate line through deaerator with waste heat recovery boiler. EFFECT: prevention of water losses caused by entraining of water by exhaust gases using deep recovery of heat with simultaneously improving performance characteristics. 3 cl, 1 dwg

Description

 The invention relates to the field of energy and can be used to create new and improve the existing combined combined cycle gas turbines (CCGT) of the contact type (CCGT-K) designed to generate electricity or as a power drive, for example, compressors of gas pumping stations of gas pipelines.

 PGU-K is known with mixing steam with combustion products: the steam received in the recovery boiler by cooling the combustion products leaving the turbine is injected into the gas path under pressure into the combustion chamber and / or into the turbine flow path. The working fluid in PSU-K is a gas-vapor mixture (ASG). Such plants are most efficient compared to conventional purely steam or gas turbine plants and combined cycle power plants, but without mixing: they surpass the best modern steam turbine plants in specific power by 20-100% or more, in efficiency by 5-10% or more at lower capital and operating costs.

The advantages of the contact cycle over the scheme without mixing - in installations with a high-pressure steam generator or with gas discharge after the turbine into the boiler, are associated with the effect of steam injection: cooling of the turbine blades, increase in the mass of the working fluid, and improvement of technical and economic indicators. Work on ASG significantly improves environmental performance: the content of nitrogen oxides NO _x in the exhaust gases decreases due to a decrease in their temperature and inhibition of the formation of these oxides in the presence of water vapor. There is a method of heat recovery in combined CCGT units with gas discharge to the boiler: the circuit includes a closed loop containing a waste heat boiler, a steam turbine with an electric generator and a condenser (see, for example, Heat Power Engineering, 1996, 4, p.5, Fig. 56).

 By utilizing the heat of the gases, electrical power is generated. However, in this and similar schemes there is no injection of steam into the gas path of the turbine and the related advantages.

 In another known method of disposal, the steam obtained in the recovery boiler is sent to the turbine (V. A. Zysin. Combined Combined Cycle Units and Cycles. M. - L.: SEI, 1962, p. 18, Fig. 1-3-3, analog). The fundamental drawback of this, as of all known solutions, is the irretrievable loss of the source water, and therefore, the need for a water source and costly water treatment.

 Saving, and, if possible, eliminating losses of cyclic water is the most important task in modern steam and gas-vapor energy, the relevance of which is increasing.

 Closest to the proposed is the technical solution proposed in the book: V.M. Maslennikov, Yu.A. Vyskubenko, V. Ya. Shterenberg (USSR), G.R. Smithson, F.L. Robson, A.V. Lemon, V.T. Lokhon (USA). Combined cycle gas turbine gasification plants and environmental problems of energy. M .: Nauka, 1983, p. 249, Fig. 12-3. This technical solution was made as a prototype.

 A combined CCGT-K implements a method that includes: air compression in a multi-stage compressor; burning fuel with steam injection in the combustion chamber; feeding the obtained ASG to the combined cycle turbine; cooling spent gas turbine in an ASG turbine in a recovery boiler-steam generator (UKPG); supply of steam from it for injection into the combustion chamber and turbine.

 The installation contains a gas circuit in which are installed in series: a multi-stage compressor; a combustion chamber and a combined cycle gas turbine equipped with steam injection devices; Combined gas turbine unit connected by steam supply pipelines for injection into the combustion chamber and turbine, as well as a deaerator for condensate degassing.

 Warm gases from the recovery boiler are released into the atmosphere along with water vapor injection.

 The task of water regeneration in this solution is not posed and is not solved, but the aim is to use the installation in peak mode, as well as to increase the useful power.

 The main objective of the invention is the elimination of water losses with exhaust gases through the deep utilization of their heat, including the complete condensation of water vapor from the ASG within the gas path. At the same time, a general improvement of technical and economic indicators is ensured - profitability, power, etc.

The problem is solved due to the fact that in a method including: compressing air in a multi-stage compressor, burning fuel with steam injection in the combustion chamber, supplying the ASG to the combined cycle gas turbine, cooling the spent ASG in the recovery boiler-steam generator (UKPG); the steam generated in it from it for injection into the combustion chamber and turbine, after the gas treatment unit the gas-vapor mixture is sent to the regenerator, while the temperature of the ASG at the inlet to it is maintained within 125-140 ^o C, and the pressure in the range 4.2-6 5 kg / cm ² ; The steam received in the regenerator is fed to a steam condensing turbine, the exhaust steam to an air condenser, and the condensate to a regenerator, while the ASG is then sent to a multi-stage turboexpander, condensate is separated along the mixture in drip moisture separators, and the condensate from the regenerator and separators is taken to condensate line and served in UKPG.

 The method is implemented in a combined-cycle plant containing a gas circuit in which a multi-stage compressor, a combustion chamber and a combined-cycle turbine are installed, equipped with steam injection devices, a gas treatment unit connected by pipelines for supplying steam to the injection into the combustion chamber and cooling the combined cycle gas turbine, as well as a deaerator for degassing condensate, additionally equipped with a closed steam-turbine circuit, including a regenerator directly behind the gas treatment plant, a steam condensing turbine and an air condenser connected to the condensate with a conduit with a regenerator, as well as a multi-stage turboexpander installed behind the regenerator with droplet moisture separators located between the steps and at the outlet, connected by a condensate line to the diaaerator.

 The essence of the invention lies in the fact that creates a closed steam-gas path in which the steam from the ASG is completely condensed. In addition, the steam-turbine circuit and multi-stage turboexpander give additional electric power, providing deep heat recovery and complete vapor condensation. When using the method, there is also an environmental effect - from reducing the content of nitrogen oxides in the exhaust gases.

 The CCGT-K scheme with condensation is especially effective in the utilization of natural gas combustion products, due to the increased content of water vapor in them and the high quality of the condensate released from the combustion products - demineralized water. It does not contain dissolved salts and is chemically pure synthetic water. After degassing, such condensate can be used as boiler feed water; other mechanical or chemical cleaning is not required.

Modern gasification technologies for low-grade fuels, including sulfur and ash coals, from obtaining a pure product open up the possibilities for the proposed CCGT-K to operate on these fuels, i.e. make their fuel base unlimited. The proposed method claims the limits of temperature and pressure of the ASG at the inlet of the regenerator: 125-140 ^o With and 4.2-6.5 kg / cm ² . They were selected empirically, confirmed by calculation and are optimal, since they simultaneously provide the greatest power of the installation and almost complete condensation of vapors in the regenerator section.

With a given range of the total pressure of the working fluid at the inlet of the regenerator 4.2-6.5 kg / cm ² , the partial pressure of water vapor in it allows almost complete completion of the condensation process within this apparatus.

When the pressure drops below 4.2 kg / cm ² the temperature of steam condensation decreases and the power of the steam turbine drops sharply, the dimensions of the heat exchangers and their cost increase. An increase in pressure above 6.5 kg / cm ² causes a decrease in the power of the main turbine and the entire installation, toughening the requirements for the strength of the regenerator and its operation, and the cost of equipment.

Similarly, with a decrease in temperature below 125 ^o C, the operation of a steam turbine sharply worsens, dimensions, metal consumption, the cost of the entire circuit, etc. increase. At temperatures above 140 ^o C, although the weight and size parameters improve and the power of the steam turbine grows, the power of the combined cycle gas turbine and the entire installation falling faster.

In the direction of flow in the regenerator there is a decrease in temperature by 25-40 ^o and pressure by 0.1-0.15 kg / cm ² .

 In addition to condensation of injection vapors, the vapors generated by the combustion of hydrogen fuel (excess water) condense in the installation. The amount of excess water can be about 0.45-0.6 kg per kg of methane burned. According to experimental data, during the combustion of 1 cubic meter. m of natural gas, consisting of methane and its homologues, about 2 cubic meters are formed. m of water vapor. With its complete condensation, 1.6 kg of water is formed and about 4000 kJ of heat is released. All this is utilized in the proposed method, increasing efficiency. Obtaining excess water is important for water-scarce facilities.

 The drawing shows a diagram of CCGT-K. A compressor 1, a combined-cycle turbine 2 with a combustion chamber 3, equipped with steam injection devices (not shown in the diagram), a recovery boiler-steam generator (UKPG) 4, a regenerator 5, a multi-stage turboexpander 6, equipped with droplet separators 7 are sequentially placed in the gas path of the installation .

 UKPG 4 and regenerator 5 are enclosed in a sealed heat-insulated chamber 8, operating under excess pressure.

 The regenerator 5, the steam turbine 9, the air condenser 10, the steam line 11 and the condensate line 12 with the pump 13 comprise a steam turbine circuit.

 Generators 14 and 15 are installed on the shafts of both turbines. The installation is equipped with a condensate drainage, collection, processing and circulation system, including separators 7, a steam trap 16 near the chamber 8 in the regenerator 5 section, a deaerator 17 and condensate pumps 18, 19, feed 20 and circulation 21 pumps connected by a common condensate line 22.

 Between the stages of the compressor 1 is installed an intermediate air cooler 23 of the contact type. The steam trap 16 is equipped with a pipe 24 with a valve for removing excess condensate.

 The method is implemented as follows.

 Outside air is sucked in and compressed in a multi-stage compressor 1, compressed air and fuel (natural gas) are supplied via line 25 to combustion chamber 3, where steam from the gas treatment unit is injected via steam line 26. The resulting ASG is sent to turbine 2, where steam is also supplied for cooling high-temperature elements. The ASG spent in the turbine is cooled sequentially in UKPG 4 and the regenerator 5. The low-pressure steam generated in it is sent through the steam line 11 to the steam turbine 9, the exhaust steam is sent to the air condenser 10, and the condensate is pumped through the condensate line 12 by the pump 13 to the inlet of the regenerator 5.

The parameters of the steam turbine (pressure before and after in the range of 0.9-0.85 and 0.098-0.13 kg / cm ² ) are such that in the air condenser 10 due to cooling of the tube bundles when blowing with a fan stream of ambient air, full condensation is ensured couple.

At the inlet of the regenerator 5 in the chamber 8, the pressure of the ASG is maintained in the range of 4.2-6.5 kg / cm ² and the temperature is 125-140 ^o C. When passing through the area of the regenerator 5, the ASG is cooled, its temperature and pressure decrease, for example, to 90-100 ^o C and 4-4.1 kg / cm ² . Under these conditions, condensation of most, more than 90%, of water vapor in the ASG occurs. The precipitated condensate is discharged from the chamber 8 to the condensate line 22 using a steam trap 16, and excess moisture is removed through the pipe 24.

 From the chamber 8, the ASG is sent to a turboexpander 6 for triggering excess pressure, and then to the separators 7 for trapping and removing the remaining condensate in the form of droplet moisture.

 From the separators 7, the condensate is pumped out by the pump 18 to the line 22, where the condensate is supplied from the condensate drain 16. Next, the condensate pump 19 is pumped under pressure into the upper part of the air cooler 23, where it is sprayed, for example, by nozzles (not shown); compressed air from the first stage of compressor 1 is supplied to the lower part. In the air cooler 23, in the process of contact heat and mass transfer of compressed air and condensate in the droplet state, the air is humidified and cooled, and sent to the second stage of compressor 1, and the condensate is pumped into the deaerator 17 by pump 21 for degassing. From here, the purified condensate is fed to UKPG 4 by a feed pump 20.

 Thus, the implementation of the claimed distinguishing features: the specified parameters of ASG in a regenerator with heat recovery in a steam turbine circuit during further utilization in a multi-stage turboexpander with moisture separation provides the technological optimum of the installation, solves the problem - complete condensation of ASG vapor at maximum power and thermal efficiency.

An example of a specific implementation of the method
Outside atmospheric air with a temperature of 15 ^o C is sucked up in an amount of 52.4 kg / s (model design mode as the most rational) in the first stage of compressor 1, where it is compressed to a pressure of 7.15 kg / cm ² , while it heats up to 263 ^o C. From the 1st stage, the air enters the intermediate cooling in the air cooler 23, condensate is sent there in the amount of 33 kg / s and sprayed with nozzles. As a result of heat and mass transfer in countercurrent, the air is cooled to 94 ^o C and served in the 2nd stage of the compressor 1, where it is compressed to 66.5 kg / cm ² .

Fuel is supplied to the combustion chamber through line 25 - natural gas, consisting mainly of methane, in the amount of 2.76 kg / s with an air flow coefficient of 1.1 and steam is injected from boiler 4 with injection parameters: flow rate of 25.6 kg / s , temperature 338 ^o C, pressure 71 kg / cm ² . Steam is also supplied to turbine 2 for cooling high-temperature elements.

At the inlet to the turbine 2, the ASG in the amount of 84.8 kg / s has a pressure of 66.5 kg / cm ² and a temperature of 1310 ^o C. The spent ASG turbine in the turbine with a flow rate of 88 kg / s, a temperature of 677 ^o C and a pressure of 4.3 kg / cm ^{2 is} sent to the chamber 8, where it gives off heat to the boiler 4 and the regenerator 5. In this case, the pressure and temperature of the ASG are maintained at 4.2 kg / cm ² and 125 ^o C; parameters at the outlet of the regenerator: 4.1 kg / cm ² and 90 ^o C (compare with the pressure on the saturation line at a temperature of 125 and 90 ^o C: 2.34 and 1.013 kg / cm ^2, respectively).

With these operating parameters, steam is generated in the regenerator with a pressure of 0.9 kg / cm ² and a temperature of 111 ^o C in an amount of 28.4 kg / s, providing a steam turbine power of 98.4 MW. The parameters of the steam behind the steam turbine 0,098 kg / cm ² with a dryness of 0.93.

From an ASG chamber 8 in an amount of 30 kg / s with a large excess pressure, they are sent to a turboexpander 6. The operation mode (number of steps) of the expander is such that at its outlet the ASG temperature does not exceed 55 ^° C, and a pressure of 1.013 kg / cm ² is sufficient to exhaust into the atmosphere. In the process of expansion of ASG in a turboexpander, further moisture is released, including excess moisture.

 Power indicators of the installation: compressor power - the first and second stages 13.3 and 23, expander 7, steam turbine 7, 9, useful electrical power of the installation 76.2 (MW).

 Efficiency gross 50.8%.

 High performance of the circuit, deep heat recovery, complete condensation in the injected steam circuit, the generation of excess water - all this indicates the high environmental and technological efficiency of the proposed solution.

Claims (2)

1. A method of heat recovery in a contact-type combined cycle gas turbine unit, including compressing air in a multi-stage compressor, supplying this air, steam and fuel to the combustion chamber, supplying the obtained gas-vapor mixture to a gas-vapor turbine, cooling the mixture exhausted in a gas-vapor turbine in a recovery boiler-steam generator , the supply of steam generated in it for injection into the combustion chamber and the combined cycle gas turbine, characterized in that the combined gas mixture after the recovery boiler-steam generator is sent to the regenerator, This mixture temperature at its inlet is maintained within 125-140 ^o C and a pressure in the range of 4,2-6,5 kg / cm ^2, the steam generated in the regenerator is fed to the condensing steam turbine and a further air supply capacitor formed in condensate to the regenerator, while the vapor-gas mixture after the regenerator is sent to a multi-stage expander, separated along the mixture in the drip moisture separators, and the condensate released in the regenerator section and from the separators is taken to the condensate line and fed to the recovery boiler steam generator.  2. A combined contact-type combined-cycle plant for implementing the method according to claim 1, comprising a gas circuit in which a multi-stage compressor is arranged, equipped with devices for injecting steam, a combustion chamber and a combined cycle gas turbine, a recovery boiler-steam generator connected by a steam supply pipe to the combustion chamber and the combined cycle a turbine and with a deaerator for condensate degassing, characterized in that it is additionally equipped with a steam turbine circuit, including a steam generator installed behind the recovery boiler a regenerator, a condensing steam turbine, an air condenser connected by a condensate line to the regenerator, and also a multi-stage turboexpander located behind the regenerator with drip moisture separators between its steps and at the outlet, connected by a condensate line to the deaerator.